Some ten years ago, The European Union established its directive 2008/50/EC “on ambient air quality and cleaner air for Europe”. It is aimed at protecting human health as well as vegetation, and it has ever since set the standard on European air quality and its monitoring.
The directive identifies sulfur dioxide (SO2), nitrogen dioxide (NO2, or more generic NOX), ozone (O3), particular matter (PM10 and PM2.5), lead (Pb), benzene (C6H6), and carbon monoxide (CO) as air pollutants to assess and attend to. The assessments are based on geographical areas called zones and agglomerations, where the population density within these areas in combination with threshold levels govern the “what” and “where”.
For all pollutants but ozone, upper and lower assessment thresholds of the pollutant concentrations have been established. In some cases, there are different sets of thresholds for different averaging periods, given that long-term and short-term exposure to a certain air pollutant can have different impacts on both human health and vegetation. The thresholds are certain percentages of limit values which are to be attained and then not to be exceeded.
The directive identifies four ambition levels of assessing air pollutant concentrations, that is the “how” in question. As a minimum, the concentrations are to be established using “objective-estimation techniques”, typically based on comparisons with other similar areas. It is also possible to model air pollution levels using databases of industrial emissions, traffic links with vehicle composition and intensity, meteorological conditions, and topography. It is deemed to be sufficient to do modelling or objective estimations of a certain pollutant concentration if the actual concentration is below the respective lower assessment threshold.
At the third ambition level, the pollutant concentrations are to be established using “indicative measurements”, which effectively means active monitoring but using somewhat relaxed quality objectives and/or limited time coverage. This is in most cases good enough for a specific parameter if the actual concentration is below the upper assessment threshold. However, going above this threshold, active monitoring must be done using “fixed measurements”. This means measurements made at fixed sites with strict quality assurance when it comes to measurement methods and data availability. The monitoring equipment must either function according to EU-specified reference methods, or be based on methods approved as equivalents to the reference methods.
Depending on the number of inhabitants within a certain zone or agglomeration, the directive then sets minimum requirements on the number of indicative or fixed monitoring points to exist within the area. However, nothing prevents a more ambitious assessment scheme to be applied, also if the actual pollutant concentrations are below the relevant thresholds – the EU directive only gives minimum requirements and member states can choose to apply a more stringent monitoring approach.
There are separate criteria for the assessment of ozone concentrations, presumably given that ozone is a secondary pollutant which concentration only indirectly is controllable by means of reduction of pollutant emissions. Instead of a limit value not to be exceeded, the directive speaks of a target value to be attained where possible. “Fixed monitoring” is required if the actual ozone concentrations are above the target value. As for the other pollutants, the directive specifies how many ozone monitoring stations there should be within a certain geographical area. At least half of the ozone monitoring stations shall also provide fixed monitoring of NO2.
The directive also states information and/or alert thresholds for SO2, NO2, and O3 concentrations representative for a certain geographical area. If the concentrations go above the specified levels, the public is to be informed using radio, television, newspapers or the Internet.
Please note that the above description is a simplified introduction to the EU directive. OPSIS has compiled are more detailed summary of both the 2008/50/EC and the 2004/107/EC directives, the latter also relevant to air quality. You can obtain a copy of this summary by clicking on this link >>.
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